A typical gas turbine includes an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section progressively increases the pressure of the working fluid and supplies a compressed working fluid to the combustion section. The compressed working fluid is mixed with a fuel such as natural gas to provide a combustible mixture. The combustible mixture is injected into a primary combustion zone defined within a combustion chamber where it is burned to generate combustion gases having a high temperature and pressure. The combustion gases are routed along through a hot gas path into the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity.
The combustion section generally includes one or more combustors annularly arranged and disposed between the compressor section and the turbine section. Various parameters influence the design and operation of the combustors. For example, gas turbine manufacturers are regularly tasked to increase gas turbine efficiency without producing undesirable air polluting emissions. The primary air polluting emissions typically produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHCs). Oxidation of molecular nitrogen and thus the formation of NOx in air breathing engines such as gas turbines is an exponential function of temperature. The higher the temperature of the combustion gases, the higher the rate of formation of the undesirable NOx emissions. However, overall gas turbine efficiency is proportional to the temperature of the combustion gases flowing through the turbine. Higher combustion gas temperatures within the turbine section corresponds to greater thermal and kinetic energy transfer between the combustion gases and various stages of rotatable turbine blades disposed within the turbine. As a result, designers are tasked with balancing emissions performance with the overall performance/power output of the gas turbine.
One system for improving overall gas turbine efficiency with minimal impact on NOx production includes one or more fuel injectors are circumferentially arranged around the combustion chamber downstream from the primary combustion zone. In operation, a portion of the compressed working fluid exiting the compressor is routed through the injectors and mixed with fuel to produce a lean (air rich) fuel-air mixture. The lean fuel-air mixture is injected into the combustion chamber downstream from the primary combustion zone where it ignites to raise the combustion gas temperature and increase the thermodynamic efficiency of the combustor. In another approach to increase efficiency, fuel may be injected into the hot gas path at a leading edge of a stationary vane or nozzle that is located at a first stage of stationary vanes or nozzles at or adjacent to an inlet to the turbine section, as described in U.S. Pat. No. 7,603,863 and assigned to the same assignee as the present invention.
Although injecting fuel through late lean injectors in the combustor section and/or stationary nozzles in the turbine section effectively increases efficiency without producing a corresponding increase in undesirable emissions, continued improvements in systems and methods of supplying fuel in a gas turbine would be useful.